Swarm Keeper is a Dungeon Keeper inspired modification for Alien Swarm. It offers the following features: Build a dungeon for your creatures (aliens), imps which perform tasks for you (like digging blocks away, collecting gold), a portal through which creatures enter your dungeon, different room types (treasure, lair, hatchery and training), a dungeon heart, which must be protected from enemies and invading marines as enemies.
This mod should be considered as an experiment to bring a Dungeon Keeper like game to the Source Engine.